The present invention relates to a method of controlling stopping operation (or shutdown operation) of a sewing machine and a system for controlling the sewing machine stopping operation. More specifically, the present invention relates to a method and a system for bringing a sewing machine from its high-speed operation into its stopped state.
Conventionally, in order to bring a sewing machine from its high-speed operation into its stopped state, as shown in FIG. 1(a), a motor employed in the sewing machine is decelerated until when its rotational speed N is decreased to a certain low level Na. After when the low speed of Na is detected, at the time t1 when a needle position sensor employed in the sewing machine detects a predetermined needle position (e.g., a lowermost needle position) H1, the motor of the sewing machine is finally decelerated to be completely stopped.
The sewing machine employing the above-described stopping operation control system, however, stops in different fashions or modes after it starts being decelerated until it finally stops at the predetermined needle position. More specifically, in a mode shown in FIG. 1(a), the lowermost needle position H2 is detected at the time t2 which is immediately before the time when the rotational speed Na is detected. Therefore, in the mode of FIG. 1(a), the motor continues to rotate at the low speed Na for about one needle stitch. In the case where the low speed Na is selected to be 200 rpm, therefore, the motor of the sewing machine has to continue to rotate at the speed of 200 rpm for a period of time L1 of about 300 ms. Accordingly, the period of time L2 from the time t0 when the sewing machine is started being decelerated to the timing t1 when the sewing machine is finally stopped becomes very long. Therefore, in the mode shown in FIG. 1(a), the stopping operation is retarded, resulting in poor operation efficiency.
On the other hand, in another mode shown in FIG. 1(b), the sewing machine can stop early, since the lowermost needle position is detected immediately after when the low speed Na is detected. In this case, the period of time L2 becomes very short.
As apparent from the above, the period of time L2 required for stopping the sewing machine depends on the relationship between the deceleration starting timing t0 and the needle position. Accordingly, different values of the period of time L2 are obtained for the respectively conducted stopping operations. In the conventional sewing machine, since the period of time L2 thus changes largely for each stopping operation, rhythms of the sewing machine stopping operation are not uniform, resulting also in poor operation efficiency.